SAN FRANCISCO — Federal regulators on Thursday approved what would be the first transplant of fetal stem cells into human brains, a procedure that if successful could open the door to treating a host of neural disorders.

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The transplant recipients will be children who suffer from a rare, fatal genetic disorder.

The Food and Drug Administration said that doctors at Stanford University Medical Center can begin the testing on six children afflicted with Batten disease, a degenerative malady that renders its young victims blind, speechless and paralyzed before it kills them.

An internal Stanford review board must still approve the test, a process that could take weeks.

The stem cells to be transplanted in the brain aren’t human embryonic stem cells, which are derived from days-old embryos. Instead, the cells are immature neural cells that are destined to turn into the mature cells that makeup a fully formed brain.

Parkinson’s disease patients and stroke victims have received transplants of fully formed brain cells before, but the malleable brain cells involved here have never before been implanted.

Batten disease is caused by a defective gene that fails to create an enzyme needed in the brain to help dispose of brain cellular waste. The waste piles up and kills healthy cells until the patient dies. Most victims die before they reach their teens.

The idea is to inject the sick kids with healthy, immature neural stem cells that will “engraft” in a brain that will direct them to turn into cells able to produce the missing enzyme.

Such an experiment showed promise in Batten-afflicted mice, but such an ethically charged test has never been tried before in humans.

“I’m sure there is no threat to anyone’s identity,” said Arthur Caplan, director of the University of Pennsylvania’s Center for Bioethics. “But we are starting down that road.”

What’s more, some of the brain cells to be implanted will be derived from aborted fetuses, which Caplan also said raised ethical concerns for some.

Stem Cells Inc., the Palo Alto, Calif. biotechnology company developing the Batten disease treatment, said it receives it fetal tissue from a nonprofit California foundation that also collects tissue from miscarriages and other surgical processes. Stem Cells chief executive Martin McGlynn declined to name the foundation.

Stem Cells Inc. first applied for the human test last December, but the FDA demanded more information in February and put the application on hold. An FDA spokeswoman didn’t return telephone calls or an e-mail inquiry.

McGlynn said the FDA wanted more information on where the transplanted brain cells were expected to go in the brain and other related health issues such as the chances the transplant might cause tumors. McGlynn also said the agency wanted more information on its manufacturing process and more details about the design of the six-patient test.

He said the FDA’s concern was expected.

“This endeavor is unique. It’s pioneering and no one has ever proposed to do what we are attempting,” McGlynn said. “Once you put those stem cells in, you can’t get them back.”

Stanford University neurosurgeon chief Dr. Stephen Huhn will bore small holes through each child’s skull and inject the neural cells into the patients’ brains. The children will be given drugs to ensure the patients immune system doesn’t attack the new cells and they will be closely monitored for a year.

Huhn said the initial Batten trial will primarily test whether the millions of new cells each child receives is safe for them. Ultimately, more tests with many more patients over several years will be needed to determine whether the transplanted cells help Batten patients.

If there is success, people afflicted by other brain disorders could benefit from such treatment.

“This may be what the future may hold for regenerative medicine,” Huhn said.

Stem Cells Inc. was founded by Stanford University researcher Irving Weissman. The company’s stock closed up 11 cents to $4.96 in trading Thursday on the Nasdaq Stock Market.

McGlynn said Batten disease was chosen because mice genetically engineered with the disease were readily available and because it’s a brutal, fatal disease with no cure — a fact the FDA considered when weighing whether to approve such a novel human experiment.

McGlynn said the stem cells had to be tested in humans.

“You cannot ask a mouse how it’s feeling,” he said.

For Marcus Kerner, a federal prosecutor in Santa Ana, Calif. with a Batten-afflicted son, the FDA’s approval Thursday gave him hope his child may actually survive.

He said he will apply to have his 5-year-old son Daniel enrolled in the experiment.

“It is a horrific, terrible way to watch a child die and there is currently nothing available to stop it,” Kerner said. “I think this is going to be a major medical breakthrough that will save Daniel’s life.”